Study On Mechanical Behavior Of Concrete-filled Square Steel Short Column With Inner CFRP I-shaped Profiles Under Axial Compression

Structure is the skeleton of high-rise buildings,which is the basis of architectural form.With the development of high-rise buildings in large space buildings and overloading requirement,the bearing capacity of columns is bigger and bigger,the structural design of bearing column relates to whether the building collapses under major earthquakes,which requires that the column should not only have enough strength but also good ductility under the condition of overloading.In order to adapt modern building structure to develop in the direction of towering,large-span,overloading and the needs of the industrialized production of construction,this paper studies the mechanical property of concret-filled square steel stube(CFST)short column with inner CFRP I-shaped profiles which is a new kind of composite structure forms proposed based on the comprehensive consideration of the disadvantages of CFST structure and FRP composite structure.This new type of composite column is the CFST column with inner CFRP I-shaped profiles,through the cooperative work among steel tube,concrete,and CFRP I-shaped profiles,the column can have bigger bearing capacity,better ductility and the purpose of fire resistance.In this paper,the development,research status and application at home and abroad of CFST structure and FRP composite structure are summarized,besides,the 30 several CFST short columns with inner CFRP I-shaped are analyzed by using nonlinear finite element methods under axial compression based on ABAQUS,and the typical components of the load-strain curves,the working mechanism of the composite column,the vertical load distribution of concrete,square steel tube,and CFRP I-shaped profiles at different stages are calculated and analyzed,the stress and strain distribution of the middle section of each component are also analyzed.In addition,the effects of the steel yield strength,concrete strength,steel ratio and CFRP profile ratio on mechanical properties of the composite column are studied,and the appropriate concrete strength and reasonable CFRP profiles ratio of this new kind of composite column are proposed.Finally,the bearing capacity calculation formula of CFST columns with inner CFRP I-shaped profiles under axial compression are deduced based on the unified theory,providing the reference for calculating the ultimate bearing capacity for the CFST columns with inner CFRP I-shaped profiles by the analysis of formula calculation results and the calculated results of finite element simulation.According to the calculation result,it shows that CFRP I-shaped profiles can significantly improve the bearing capacity and ductility at the basic of ordinary CFST column.Concrete undertake the main part of the vertical load,before the composite column reaches the ulimate state,after arriving the ultimate bearing capacity state,steel pipe separate conveys basic remain unchanged,but the concrete and CFRP i-section profile alone bear the load shift trends,CFRP I-shaped profiles occur brittle failure along with large deformation of the columns,integral component rapidly reduced load surface.The constraint of square steel tube to concrete are mainly concentrated at the corner,concrete occur high strength at the flange part of CFRP CFRP profiles,CFRP I-shaped profiles delayed the macroscopic crack of concrete,improve the bearing capacity and ductility of the member.With the increase of steel strength,the bearing capacity increases gradually,but the pace expansion decreases.The higher the concrete strength is,the increase of ultimate bearing capacity is more obvious,but the ductility of the member decrease.The bigger the steel ratio is,the bearing capacity of components increase more obvious,and the ductility increase.With CFRP profiles ratio improve,the bearing capacity of components significantly raise,while keeping the load strain curve strengthening phenomenon more and more obvious.Based on ordinary steel pipe constraint to normal concrete,the suitable concrete strength are C30 and C40,economic reasonable CFRP profiles is from 4%to 10%.Based on unified theory,bearing capacity calculation formula calculation results of concrete filled steel tube columns with inner CFRP I-shaped profiles are in good agreement with those obtained in the simulation.In this paper,the research results can to provide a reference for further research of this new type composite column.